Abstract
Land use, habitat, and forage quality have emerged as critical factors influencing the health, productivity, and survival of honey bee colonies. However, characterization of the mechanistic relationship between differential land-use conditions and ultimate outcomes for honey bee colonies has been elusive. We assessed the physiological health of individual worker honey bees in colonies stationed across a gradient of agricultural land use to ask whether indicators of nutritional physiology including glycogen, total sugar, lipids, and protein were associated with land-use conditions over the growing season and colony population size the subsequent spring during almond pollination. Across the observed land-use gradient, we found that September lipid levels related to growing-season land use, with honey bees from apiaries surrounded by more favorable land covers such as grassland, pasture, conservation land, and fallow fields having greater lipid reserves. Further, we observed a significant relationship between total protein during September and population size of colonies during almond pollination the following February. We demonstrate and discuss the utility of quantifying nutritional biomarkers to infer land-use quality and predict colony population size.
Highlights
Managed honey bees are wide-ranging, generalist-foraging, social organisms that primarily rely on environmentally-available resources to support the growth, productivity, and survival of their colonies
Protein levels exhibited a positive relationship with colony population size in almonds (F1,34 = 6.38, r2 = 0.16, p = 0.02), meaning apiaries containing colonies and bees with higher September protein levels were larger for almond pollination (Fig. 3)
Consistent with our previous work[14], we found land use across the studied agricultural gradient to be related to colony population size in almond orchards during pollination (Row crops: F1,34 = 24.92, r2 = 0.42, p < 0.0001; Grassland: F1,34 = 21.61, r2 = 0.39, p < 0.0001). meaning 42% of the variation in population size among apiaries during almond pollination could be attributed to summer row crop land use conditions, with greater areas of row-crop agriculture resulting in smaller population sizes for almond pollination (Fig. 4)
Summary
Managed honey bees are wide-ranging, generalist-foraging, social organisms that primarily rely on environmentally-available resources to support the growth, productivity, and survival of their colonies. Access to forage resources growing across the region support population growth and honey production throughout the summer[9,10,11] Many of these summering colonies, after overwintering in various locations across the country, go on to pollinate almonds in the Central Valleys of California in early spring. Because little to no forage is available to honey bee colonies from October–February, resource (pollen and nectar) availability and land-use conditions across the NGP region during the summer directly impact honey bee colony robustness for almond pollination, setting the stage for successful overwintering and resulting robust, healthy colonies to meet early spring pollination-service demands[9,14]. We examined the nutritional status of individual honey bees in the context of varying land-use conditions in the NGP to elucidate the nutritionally-mediated impacts of land use on honey bee health.
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